Abnormal collections of fluids in a body cavity of an individual, referred to as effusions, are often caused by malignant tumors. An effusion can also be the first sign that a tumor which had been surgically removed or had undergone remission is metastasizing. However, an effusion can have many causes that are unrelated to cancer, e.g. heart failure, liver dysfunction and pneumonia. Presently, the standard method of determining whether an effusion is caused by a cancer from an effusion resulting from other causes is to remove some of the effusion fluid, isolate the cells contained therein, and examine the cells morphologically. However, this method of diagnosis leaves a significant percentage of cancers undetected. A more reliable method of determining whether an effusion is cancer-related would allow earlier intervention with treatment and can increase the likelihood of better clinical outcomes.
In many cases it is difficult to determine whether a tumor or nodule is malignant without surgically removing the suspected tissue. For example, when a thyroid nodule is detected, one method for distinguishing benign from malignant nodules is cytologic examination of cells obtained by fine needle aspiration (FNA). Routine cytologic examination of FNA specimens is, however, far from satisfactory. Even when adequate specimens are obtained the cytologic report is often indeterminate because of the inherent inability of routine cytology to distinguish benign from malignant follicular neoplasms (adenoma vs. carcinoma) when a microfollicular pattern is seen. This frequently leads to surgical excision of these nodules, the majority of which are ultimately found to be benign (Mazzaferri, E. L., New Engl. J. Med. 328:553-559, 1993). In addition, concern about false-negative reports when the cytologic diagnosis is benign may also lead to surgery. As a result, the majority of patients who have thyroid surgery for nodules turn out to have benign disease, even with the extensive use of FNA and routine cytology (Mazzaferri, E. L., Am. J. Med. 93:359-362, 1992; Cusick, et al., Br. Med. J. 301:318-321, 1990). Consequently, there is a need for a more accurate method of distinguishing between malignant and benign tumors prior to surgery.